Conventionally, as a detection method for a pointer such as a finger of a user or a pen for exclusive use with a touch panel or the like, various sensor methods have been proposed such as, for example, an electrostatic coupling method (capacitance method), a resistive film method, and an electromagnetic induction method.
In a pointer detection apparatus of the electrostatic coupling method, as shown in FIG. 59, a plurality of upper electrodes Ex and a plurality of lower electrodes Ey are juxtaposed, for example, in an X-axis direction (lateral direction) and a Y-axis direction (longitudinal direction) of the pointing input surface and are arrayed orthogonally to each other and in a spaced relationship from each other with a small gap left therebetween. Consequently, a predetermined capacitor Co is formed at an overlapping location of each upper electrode Ex and each lower electrode Ey.
In the pointer detection apparatus of the electrostatic coupling method of FIG. 59, if a pointer such as a finger of a user approaches or touches the pointing input surface, then a capacitor Cf is formed between the pointer and the upper electrode Ex at the location. As a result, the amount of movement of charge between the upper electrode Ex and the lower electrode Ey at the location varies. In the pointer detection apparatus of the electrostatic coupling method, the variation of the amount of movement of charge is detected to specify the position in the pointing input surface pointed to by the pointer.
A pointer detection apparatus of the electrostatic coupling method of the type described above is disclosed, for example, in Patent Documents 1 to 3 listed below. In Patent Document 1, a technique of applying a code division multiplexing method which uses orthogonal spread codes to a multi-user touch system is disclosed. In Patent Document 2, a coordinate inputting apparatus which uses a pseudorandom signal is disclosed. Further, in Patent Document 3, an electrostatic pen used with a capacitive type coordinate apparatus is disclosed.
Meanwhile, in regard to pointer detection using the resistive film method, particularly a technique for detecting a plurality of pointing inputs is disclosed, for example, in Patent Document 4. The pointer detection technique using the resistive film method disclosed in Patent Document 4 is described with reference to FIG. 60.
In particular, the pointer detection apparatus of Patent Document 4 includes an electrode sheet 1001 on which a plurality of upper electrodes Ex similar to those of the example of FIG. 59 are formed, a first resistive element layer 1002, a second resistive element layer 1003, and an electrode sheet 1004 on which a plurality of lower electrodes Ey similar to those of the example of FIG. 59, which are arrayed in a laminated relationship in a z-axis direction orthogonal to an x axis and a y axis.
In this instance, as shown in FIG. 60(B) which is a sectional view of FIG. 60(A), the first resistive element layer 1002 is formed on the upper electrodes Ex formed on the electrode sheet 1001 such that the upper electrodes Ex and the first resistive element layer 1002 are electrically connected to each other. Further, the second resistive element layer 1003 is formed on the lower electrodes Ey formed on the electrode sheet 1004 such that the lower electrodes Ey and the second resistive element layer 1003 are electrically connected to each other. A very small air gap AG is formed between the first resistive element layer 1002 and the second resistive element layer 1003.
In the pointer detection apparatus of this case, if a pointing input surface, that is, the electrode sheet 1001 in the example shown, is pressed in the Z-axis direction by a pointer such as a finger, then the electrode sheet 1001 is elastically displaced at the pressed portion thereof until the first resistive element layer 1002 and the second resistive element layer 1003 are brought into contact with each other as shown in a sectional view of FIG. 60(C). Then, as the pressing force from the pointer to the pointing input surface increases, the contact area between the first resistive element layer 1002 and the second resistive element layer 1003 increases.
Consequently, a variable resistor in accordance with the contact area between the first resistive element layer 1002 and the second resistive element layer 1003 is interposed between the upper electrode Ex and the lower electrode Ey at the pressed portion. In this instance, the resistance of the variable resistor decreases as the contact area between the first resistive element layer 1002 and the second resistive element layer 1003 increases. It is to be noted that, when the pointing input surface is not pressed by a pointer as in FIG. 60(B), the first resistive element layer 1002 and the second resistive element layer 1003 are almost in a non-contacting state with each other, and therefore, the resistance of the variable resistor is almost infinite.
Accordingly, even if a voltage is applied through one of the upper electrode Ex and the lower electrode Ey in the state of FIG. 60(B), signal current of the voltage is not transmitted to the other electrode. Then, if the first resistive element layer 1002 and the second resistive element layer 1003 are brought into contact with each other, signal current from one of the electrodes begins to flow to the other electrode through the variable resistor. Then, if the contact area between the first resistive element layer 1002 and the second resistive element layer 1003 increases as the pressing force increases, then the signal current flowing from the one electrode to the other electrode increases in response to the contact area.
From the foregoing, in the pointer detection apparatus of the resistive film method, if the variation in resistance value between the upper electrode Ex and the lower electrode Ey is detected, then the position pointed to by the pointer can be specified and the pressing force is detected from the resistance value of the resistor.